Comets don’t explain weird behavior of ‘alien megastructure’ star

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There’s a mystery afoot in the constellation Cygnus, and it’s one we thought we had figured out. The star known as KIC 8462852 made news a few months ago when its unusual pattern of dimming led some to speculate that intelligent life could be to blame — so-called “alien megastructures.” The accepted explanation of its odd behavior was a swarm of dusty comets, but a new analysis calls that into question. So, what is going on around KIC 8462852?

The mystery begins when the Kepler space telescope surveyed KIC 8462852 (about 1480 light years away) in its search for potential exoplanets. Kepler uses the transit method to spot planets around distant stars. When an object (like a planet) passes between its parent star and Earth, there’s a tiny drop in luminance. By recording the frequency and magnitude of this drop, we can infer things about the planet. KIC 8462852 wasn’t behaving like a star with exoplanets, though. It was flickering seemingly at random.

There were two explanations put forward for this unusual behavior. The first (and let’s face it, more plausible) was a swarm of dusty comets in orbit of the star that blocked some of its light. The more interesting hypothesis was the presence of alien megastructures in orbit of the star, possibly designed to collect solar energy. Neat, right? Unfortunately, neither of these ideas is holding up to more rigorous examination.

Astronomer Bradley Schaefer of Louisiana State University used data from long-term observations taken at Harvard to track the behavior of KIC 8462852. Perhaps there was more going on than just the random dips in luminance? The university has photographic plates of the sky dating back more than a century, and they show that the star dimmed by 20% between 1890 and 1989 — Schaefer even went to Harvard himself to confirm the data by reading the plates manually.

Based on that new/old data, Schaefer calculated that there would need to be 648,000 comets, each 200 kilometres wide in orbit of KIC 8462852. That’s simply not plausible based on what we know about solar systems. So what of the alien megastructure idea? Perhaps there’s someone out there progressively building more objects in orbit of KIC 8462852. Again, this doesn’t fully explain the readings. Even if you assume an alien society has the ability to build objects that block a fifth of the light from a star (possibly on the way to a Dyson Sphere?), there’s no heat signature from it. Anything that absorbs that much light should radiate some of that out as infrared.

KIC 8462852 is still a genuine mystery. Schaefer is careful not to rule out either of the proposed explanations, as there could be some angle he and his team didn’t consider. Whatever is going on, it requires more study.

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